Storage tank heating arrangement

ABSTRACT

A cylindrical tank car has on the underside thereof a centrally disposed lading outlet and a heating arrangement which comprises an input manifold assembly extending longitudinally the length of the tank bottom and including a central rectangular input section circumscribing the lading outlet, two intermediate sinuous coil sections respectively communicating with opposite ends of the rectangular section, and two end manifold sections, a circumferentially extending output manifold midway between the tank ends cooperating with the input manifold assembly to divide the tank bottom into four areas, each area having a group of heating coils communicating with the adjacent input manifold section and with the output manifold; heating fluid is supplied to the rectangular input section and withdrawn from the output manifold.

United States Patent [72} Inventors Erling Mowatt-Larssen Warren, Ohio; William A. Taylor, Sharpsville, Pa. [211 App]. No. 858,794 [22] Filed Sept. 17, 1969 [45] Patented July 27, 1971 [73] Assignee General American Transportation Corporation Chicago, Ill.

[54] STORAGE TANK HEATING ARRANGEMENT 20 Claims, 6 Drawing Figs.

[52] [1.8. CI 165/47, 165/169 {51) Int. Cl F24h 7/02 [50] Field ofSearch 165/47,

[56] References Cited UNITED STATES PATENTS 3,228,466 1/1966 Carleton 165/169 Primary Examiner-Charles Sukalo Assistant Examiner-W. C. Anderson Attorney-Prangley, Clayton, Mullin, Dithmar and Vogel ABSTRACT: A cylindrical tank car has on the underside thereof a centrally disposed lading outlet and a heating arrangement which comprises an input manifold assembly extending longitudinally the length of the tank bottom and including a central rectangular input section circumscribing the lading outlet, two intermediate sinuous coil sections respectively communicating with opposite ends of the rectangular section, andtwo end manifold sections, a circumferentially extending output manifold midway between the tank ends cooperating with the input manifold assembly to divide the tank bottom into four areas, each area having a group of heating coils communicating with the adjacent input manifold section and with the output manifold; heating fluid is supplied to the rectangular input section and withdrawn from the output manifold.

SHEET 2 [1F 3 STORAGE TANK HEATING ARRANGEMENT This invention relates in general to storage tanks. More particularly, it relates to external arrangements for heating such tanks and the lading contained therein.

It is a general object of this invention to provide an improved apparatus for heating the contents of a storage tank to improve the flow characteristics thereof under low ambient temperatures. An important object of this invention is to provide an improved heating arrangement for storage tanks wherein the most intense heating is achieved along the bottommost portion thereof and, in particular, adjacent to the lading outlet. Another object of this invention is to provide a heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into the lading compartment, output means in the bottom of the wall structure for emptying lading from the lading compartment, an input manifold carried by the bottom of the wall structure, an output manifold carried by the bottom of the wall structure and crossing over the input manifold intermediate the ends thereof, a plurality of heating coils carried by the wall structure adjacent to the bottom thereof, each of the heating coils communicating with the input manifold and the output manifold, means for introducing heating fluid into the input manifold, and means for withdrawing spent heating fluid from the output manifold, whereby heating fluid is carried from the input manifold through the heating coils to the output manifold for heating the bottom of the storage tank and the lading contained therein.

In connection with the foregoing object, it is another object of this invention to provide a heated storage tank of the character described, wherein the output manifold crosses over the input manifold intermediate the ends thereof, the input manifold and the output manifold cooperating to define four sectors on the bottom of the wall structure, and wherein the heating coils are divided into four groups, each of the groups being limited to a different one of the sectors and communicating with the input manifold and the output manifold.

In connection with the foregoing objects, yet another object of this invention is to provide a heated storage tank of the character described, wherein the heating coils include a plurality of primary heating coils carried by the bottom of the wall structure and disposed in surrounding relationship with the output means and each having an inlet and an outlet, and a plurality of secondary heating coils carried by the wall structure and disposed adjacent to the primary heating coils and each having an inlet and an outlet, and further including input manifolds interconnecting the outlets of the primary heating coils and the inlets of the secondary heating coils, and an output manifold interconnecting the outlets of the secondary heating coils, whereby heating fluid is carried first to the primary heating coils and thence through the input manifold to the secondary heating coils and thence to the output manifolds for heating the bottom of the storage tank and the lading contained therein with the most intense heating being adjacent to the output means.

In connection with the foregoing object, it is another object of this invention to provide a heated storage tank of the character described, wherein there are two primary heating coils, and further including a pair of connecting coils carried by the bottom of the wall structure adjacent to the output means and interconnecting the inlets of the two primary heating coils.

In connection with the foregoing object, still another object of this invention is to provide a heated storage tank of the character described wherein each of the two primary heating coils has an inlet and a pair of outlets and wherein the secondary heating coils are divided into four groups each of the groups including the same predetermined number of coils and each of the coils having an inlet and an outlet, and further including four input manifolds carried by the wall structure and each having an inlet and a plurality of outlets equal in number to the predetermined number, the inlets of the input manifolds respectively communicating with the outlets of the first and second primary heating coils, and the outlets of each of the inputmanifolds respectively communicating with the inputs of a different one of the four groups of secondary heating coils.

Yet another object of this invention is to provide a heated storage tank comprising an encompassing cylindrical sidewall disposed substantially horizontally, two end walls respectively closing the opposite ends of the sidewalls, the cylindrical sidewall and the end walls cooperating to define a closed lading compartment, input means for introducing lading into the lading compartment, output means disposed in the bottom of the cylindrical sidewall midway between the ends thereof for emptying lading from the lading compartment, first and second primary heating coils carried by the bottom of the cylindrical sidewall and disposed symmetrically with respect to the vertical midplane thereof adjacent to the output means and each having an inlet and a pair of outlets, each of the primary heating coils including a plurality of interconnected straight sections extending longitudinally of the cylindrical sidewall, a pair of connecting coils carried by the bottom of the cylindrical sidewall and disposed longitudinally thereof on opposite sides of the output means and interconnecting the inlets of the first and second primary heating coils, four groups of secondary heating coils carried by the cylindrical sidewall and disposed adjacent to the primary heating coils, each of the groups including the same predetermined number of coils and each of the coils being disposed substantially longitudinally of the cylindrical sidewall and having an inlet and an outlet, means for introducing heating fluid into the inlets of the primary heating coils, four input manifolds carried by the cylindrical sidewall and extending longitudinally thereof and each having an inlet and a plurality of outlets equal in number to the predetermined number, the inlets of the input manifolds respectively communicating with the outlets of the first and second primary heating coils, the outlets of each of the input manifolds respectively communicating with the inputs of a different one of the four groups of secondary heating coils, an output manifold carried by the cylindrical sidewall and extending circumferentially thereof midway between the ends thereof and interconnecting the outlets of the four groups of secondary heating coils, and means for withdrawing spent heating fluid from the output manifold, whereby heating fluid is carried first to the primary heating coils and connecting coils and thence through the input manifolds to the secondary heating coils and thence to the output manifold for heating the bottom of the storage tank and the lading contained therein with the most intense heating being adjacent to the output means.

In connection with the foregoing object, it is another object of this invention to provide a vehicle comprising a wheeled chassis, carrying thereon a heated storage tank of the character described.

The invention, both as to its organization and its method of operation together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevational view of a railway tank car according to this invention showing one-half of the external heating arrangement;

FIG. 2 is a bottom plan view of the external heating arrangement ofthe tank car shown in FIG. 1;

FIG. 3 is a fragmentary view in partial section taken along the line 3-3 in FIG. 2 and showing the heating fluid outlet pipe;

FIG. 4 is a fragmentary view in partial section taken along the line 4-4 in FIG. 2 and showing the heating fluid input apparatus;

FIG. 5 is a fragmentary sectional view taken along the line 5-5 in FIG. 2; and

FIG. 6 is a fragmentary sectional view taken along the line 6-6 in FIG. 2.

Referring now to the drawings, there is shown in FIG. 1 a railway tank car, generally designated by the numeral 50, and comprising a relatively long, horizontally disposed cylindrical sidewall 55, the opposite ends thereof being respectively closed by a pair of generally concave head members 57 and 59, the cylindrical sidewall and the head members 57 and 59 cooperating to form a tank 60 defining therein an enclosed lading compartment. In the top of the cylindrical sidewall 55, adjacent to the center thereof, are a pair of lading input hatches 65, respectively disposed on opposite sides of the vertical midplane of the cylindrical sidewall 55 normal to the longitudinal axis thereof. The tank 60 is supported adjacent to the opposite ends thereof by a pair of standard truck and wheel assemblies 70, the truck and wheel assemblies being coupled to the tank 50 by means of bolsters and bolster plates or saddles in the conventional manner. A pair of lading drain valve units and 95, each communicating with the lading compartment, are disposed in the bottom of the cylindrical sidewall 55 adjacent to and on opposite sides of the vertical midplane thereof normal to the longitudinal axis thereof. The valve units 90 and are respectively provided with caps, as at 91, for closing the valve units 90 and 95 when not in use. In operation, lading is introduced into the tank 60 through the lading input hatches 65 and is withdrawn from the tank 60 through the lading outlet valve units 90 and 95 under the action of gravity. Any number of different types of lading may advantageously be carried in the tank 60, both those which are normally in the liquid state at ambient temperatures, e.g., vegetable and mineral oils, corn syrup and various chemical compounds, and those which are normally in the solid stage at ambient temperatures, e.g., paraffin, lard, etc. However, for effective unloading through the valve units 90 and 95 these various ladings must all be placed in a freely flowing liquid stage, which can usually be accomplished by elevating their temperatures.

Arranged on the outer surface of the bottom of the cylindrical sidewall 55 is a heating assembly, generally designated by the numeral 100. The heating assembly is symmetrical with respect to the vertical midplane of the cylindrical sidewall 55 normal to the longitudinal axis thereof and, therefore, only the left-hand portion thereof, as viewed in FIG. 2, will be described in detail, it being understood that the righthand portion thereof as viewed in FIG. 2 is simply a mirror image of the left-hand portion. Referring to FIG. 2, and in par ticular to the left-hand portion thereof, the heating assembly 100 comprises a relatively short input channel disposed adjacent to the outer edge of the valve unit 90 and extending circumferentially of the cylindrical sidewall 55. The input channel 105 is closed at the opposite ends thereof by end plates or caps 106. The input channel 105 is symmetrical with respect to a vertical plane passing through the longitudinal axis of the cylindrical sidewall 55. Communicating with the input channel 105 midway between the ends thereof, and extending longitudinally of the cylindrical sidewall 55 to the left as viewed in FIG. 2 is a primary heating coil assembly, generally designated by the numeral 110. The primary heating coil assembly includes a first straight section 112 extending longitudinally of the cylindrical sidewall 55 along the bottom thereof, and communicating at its inner end with the input channel 105 and at its outer end with a short, arcuate, circumferentially extending end section 115, midway between the ends thereof. The opposite ends of the end section 115 respectively communicate with a pair of straight sections 116 and 117 extending longitudinally inwardly of the cylindrical sidewall 55 parallel to the straight section 112 to points adjacent to the input channel 105v The inner ends of the straight sections 116 and 117 respectively communicate with a pair of short, arcuate, circumferentially extending end sections 118 and 119 which respectively extend to points adjacent to the end caps 106 ofthe input channel 105.

The outer ends ofthe short end sections 118 and 119 in turn communicate, respectively, with a pair of input manifolds 120 and extending longitudinally outwardly of the cylindrical sidewall 55 to points adjacent to the end head 57. The input manifolds 120 and 130 are respectively closed at the outer ends thereof by the end caps 121 and 131. Arranged circumferentially outwardly of the input manifold 120 is a secondary heating coil assembly, generally designated by the numeral 125, and comprising a plurality of secondary heating coils 126, six of such coils being shown in FIG. 2. Each of the secondary heating coils 126 comprises a relatively short, arcuate, circumferentially extending portion 127 integral with a relatively long straight longitudinally extending portion 128. The secondary heating coils 126 are so arranged that the short circumferential portions 127 thereof are spaced apart longitudinally of the cylindrical sidewall 55 and are each connected to the input manifold 120 adjacent to the outer end thereof for providing communication therewith. The lengths of the circumferential portions 127 of the secondary heating coils 126 increase progressively from right to left, as viewed in FIG. 2, whereby the longitudinal portions 123 of the secondary heating coils 126 may be spaced apart circumferentially of the cylindrical sidewall 55.

Another secondary heating coil assembly, generally designated by the numeral 135, is arranged circumferentially outwardly of the input manifold 130 and comprises a plurality of secondary heating coils 136, preferably equal in number to the number of the secondary heating coils 126. Each of the secondary heating coils 136 comprises a relatively short, arcuate, circumferentially extending portion 137 integral with a relatively long, straight, longitudinally extending portion 138. The secondary heating coils 136 are so arranged that the relatively short circumferentially extending portions 137 thereof are spaced apart longitudinally of the cylindrical sidewall 55 and are each connected to the input manifold 130 adjacent to the outer end thereof for providing communication therewith. The lengths of the circumferentially extending portions 137 of the secondary heating coils 136 increase progressively from right to left as viewed in FIG. 2, whereby the longitudinal portions 138 of the secondary heating coils 136 may be spaced apart circumferentially of the cylindrical sidewall 55. The secondary heating coil assemblies 125 and are preferably arranged symmetrically with respect to the vertical plane passing through the longitudinal axis of the cylindrical sidewall 55.

Midway between the ends of the cylindrical sidewall 55 is a circumferentially extending output manifold 140, closed at the opposite ends thereof by end caps 141. The output manifold 140 has a pair of radially extending sidewalls 142 integral with and connected by a generally concave bottom wall 143 as can best be seen in FIG. 6. The inner ends of each of the longitudinal portions 128 and 138 of the secondary heating coils 126 and 136 communicate with the output manifold 140. It will, of course, be understood that the output manifold 140 also communicates with the secondary heating coils 126 and 136 in the right-hand half of the heating assembly 100, as viewed in FIG. 2.

A pair of connecting channels 145 and 146 are provided adjacent to the lading drain valve units 90 and 95, the connecting channels 145 and 146 extending longitudinally of the cylindrical sidewall 55 and respectively interconnecting the opposite ends of the input channels 105. More particularly, the connecting channel 145 interconnects the upper ends of the input channels 105 as viewed in FIG. 2, and the connecting channel 146 interconnects the lower ends of the input channels 105 as viewed in FIG. 2, thereby providing communication between the two input channels 105. It will be noted that the input channels 105 and the connecting channels 145 and 146 cooperate to provide a generally rectangular coil arrangement completely circumscribing the lading drain valve units 90 and 95 in close proximity thereto. Further, it is noted that the output manifold 140 does not intersect the connecting channels 145 and 146, but rather crosses beneath them, as shown in FIG. 6.

Each of the input channels 105, the primary heating coil sections 112,115,116, 117,118 and 119, the input manifolds 120 and 130, the secondary heating coil portions 127 and 128, and the connecting channels 145 and 146 comprises a pair of relatively short, radially extending sidewalls indicated at 123 in FIG. 5, integral with and connected by a generally concave bottom wall, indicated at 124 in FIG. 5. However, the crosssectional areas of the secondary heating coils 126 and 136 are substantially smaller than the cross sectional areas of the other portions of the heating assembly 100, as is also best shown by FIG. 5. This difference in cross-sectional areas is for the purpose ofmaintaining the heating fluid pressure in the secondary heating coil assemblies 125 and 135 substantially the same as in the rest of the heating assembly 100, since there are six secondary heating coils communicating with each input manifold.

Heating fluid is introduced into the heating assembly 100 by means of heating fluid inlet apparatus, generally designated by the numeral 150, as can best be seen in FIG. 4. The heating fluid inlet apparatus 150 includes a steam jacket 151 surrounding the lading drain valve unit 90 and having an inlet nozzle 152 and an outlet nozzle 153. Communicating with the inlet nozzle 152 is a jacket inlet pipe section 154 extending downwardly from the jacket 151 at an acute angle thereto. The jacket inlet pipe section 154 is threadedly coupled to a vertical pipe section 155 by means of an internally threaded elbow joint 156. Threadedly engaged with the pipe section 155 at the bottom end thereof is an end cap 158 for closing the heating fluid inlet apparatus 150 when not in use. Communicating with the outlet nozzle 153 of the steam jacket 151 is a horizontally extending jacket outlet pipe section 160, the pipe section 160 being threadedly coupled to a vertically extending pipe section 161 by means of an internally threaded elbow joint 162. The vertical pipe section 161 is coupled to the bottom of the left-hand one of the input channels 105, midway between the ends thereof, by means of an adapter fitting 163. If desired, the valve unit 95 may be jacketed in this same manner.

A heating fluid outlet apparatus, generally designated by the numeral 170, is provided in the bottom wall 143 of the outlet manifold 140, midway between the ends thereof. Referring to FIG. 3 of the drawings, the heating fluid outlet apparatus 170 includes a downwardly, vertically extending outlet pipe 172 coupled to the bottom wall 143 of the output manifold 140 by means of an adapter fitting 174. Threadedly engaged with the bottom end of the outlet pipe 172 is an end cap 175 for closing the heating fluid outlet apparatus 170 whennot in use.

There may also be provided in the bottom wall of the lefthand one of the input channels 105 as viewed in FIG. 2, a plurality of auxiliary heating fluid inlet assemblies, two such assemblies 180 and 185 being shown in FIG. 2 disposed adjacent to the heating fluid inlet apparatus 150 on either side thereof. Each of the auxiliary inlet assemblies 180 and 185 is preferably identical in construction to the heating fluid outlet apparatus 170 as described above in connection with FIG. 3. An additional inlet-outlet opening 190 is provided in the bottom wall of the right-hand one of the input channels 105 as viewed in FIG. 2, midway between the ends thereof. This opening 190 may be used as an outlet for purging the heating apparatus 100 of air at the beginning of the heating process or, alternatively, as an additional inlet for heating fluid.

In operation, a source of suitable heating fluid, such as steam, is connected to the lower end of the pipe section 155 of the heating fluid inlet apparatus 150, after the end cap 158 has been removed therefrom. Heating fluid then passes through the inlet pipe sections 155 and 154 to thesteam jacket 151 for directly heating the lading drain valve unit 90. The heating fluid then passes from the steam jacket 151 through the outlet pipe sections 160 and 161 into the left-hand one of the input channels 105 of the heating assembly 100 as viewed in FIG. 2. The heating fluid then branches into three paths, one directly into the longitudinal section 112 ofthe left-hand primary heating coil assembly 110, and the others into the connecting channels 145 and 146 and thence to the right-hand one of the input channels 105 and thence to the longitudinal section 112 of the right-hand one of the primary heating'coil assemblies 110. The path of the heating fluid through the left and righthand heating coil assemblies is identical and, therefore, will be described in detail only with respect to the left-hand portion of the heating assembly as viewed in FIG. 2. From the longitudinalsection 112 of the primary heating coil assembly 110, the heating fluid passes into the circumferential end section 115 and thence to, the longitudinal sections 116 and 117. From the longitudinal sections 116 and 117, the heating fluid passes through the short end sections 118 and 119, respectively, into the input manifolds 120 and 130. The heating fluid then passes through the input manifolds 120 and into the circumferential portions 127 and 137 of the secondary heating coils 126 and 136, respectively. Then, the heating fluid passes through the longitudinal portions 128 and 138 of the secondary heating coils 126 and 136 into the output manifold 140, then drains from the output manifold 140 through the heating fluid outlet apparatus 170, from which the end cap will have been removed. The outlet pipe 172 of the heating fluid outlet apparatus 170 may be vented to the atmosphere or, alternatively, may be connected to a suitable heating fluid collecting apparatus or recycled to the source of heating fluid. It will, of course, be understood that the heating fluid path is exactly the same through the right-hand portion of the heating assembly, this portion also emptying into the output manifold, 140 and thence to the heating fluid outlet apparatus 170 as described above.

In lieu of, or in addition to the heating fluid inlet apparatus 150', the auxiliary inlet assemblies and may be used to introduce heating fluid to the heating assembly 100. When used in addition to the heating fluid inlet apparatus 150, the inlet assemblies 180 and 185 will respectively channel the heating fluid directly to the connecting channels 145 and 146, while the heating fluid inlet apparatus 150 will channel the heating fluid directly to the left-hand ones of the primary heating coil assemblies 110. Also, the auxiliary opening may be used to introduce heating fluid more directly into the righthand portion of the heating assembly 100 for more even heating of the right and left-hand portions of the storage tank 60. It will, of course, be appreciated that when all of the various heating fluid inlet devices are used simultaneously, greater input of heating fluid to the heating assembly 100 can be achieved with a corresponding reduction in heating time. When not used as an auxiliary heating fluid input, the opening 190 is normally used for purging air from the heating assembly 100 at the initiation of the heating process.

The various portions of the heating assembly 100 are preferably all formed of the same material, which may advantageously be metal, and are all secured to the outer surface of the cylindrical sidewall 55 as by welding. It will be noted that except in the areas where the various coil and manifold sections cross over each other, they comprise only sidewalls and bottom walls, the cylindrical sidewall 55 of the tank is providing the top wall of the various channels through which the heating fluid flows, thereby providing direct contact between the heating fluid and the cylindrical sidewall 55 to facilitate the passage of heat therebetween.

One of the primary advantages of this invention, is the even distribution of heat along the bottom of the tank 60. The centrally located inlet of the heating fluid in close proximity to the lading drain valve units 90 and 95 provides the greatest concentration of heat in the immediate vicinity of the lading drain valve units to insure the free flow oflading therethrough. This intense heating of the valve units is further enhanced by steam jacketing of at least one of these valve units as described above in connection with FIG. 4. Further, the centrally located heating fluid inlet, in cooperation with the longitudinal arrangement with the primary heating coils and input manifolds provides for an even distribution of heat to both ends of the tank 60 simultaneously, the most intense heat being applied directly to the bottommost portion thereof. This intense heating of the bottommost portion of the tank 60 is desirable for facilitating convection currents in the lading,

whereby the hot lading along the bottom of the tank moves upwardly through the colder lading overlying it, thereby dispersing heat upwardly through the lading. After having cooled somewhat in its passage along the bottom of the tank 60, the heating fluid is then passed through the secondary heating coil assemblies 125 and 135 to the output manifold 140, thereby heating the portions of the sidewalls 55 lying above the bottommost portion.

An additional advantage of the input manifolds having a longitudinal extent running to the ends of the cylindrical sidewall 55 is that it permits ready access to the end heads 57 and 59 for heating thereof. For this purpose, additional heating coils may be coupled to the input manifolds 120 and 130 and disposed on the outer surfaces of the end heads 57 and 59 for direct heating thereof.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What we claim is:

1. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, an input manifold carried by the bottom of said wall structure, in close proximity to said output means, an output manifold carried by the bottom of said wall structure and crossing over said input manifold intermediate the ends thereof, said input manifold and said output manifold cooperating to define four sectors on the bottom of said wall structure, four groups of heating coils carried by said wall structure adjacent to the bottom thereof and being arranged on a substantial part of the bottommost portion ofsaid wall structure, each of said groups of coils being limited to a different one of said sectors and communicating with said input manifold and said output manifold, means for introducing heating fluid into said input manifold, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried from said input manifold through said heating coils to said output manifold for heating the bottom of said storage tank and the lading contained therein.

2. The storage tank set forth in claim 1, wherein said input manifold and said output manifold are disposed substantially perpendicular to each other, said manifolds crossing each other midway between the ends thereof.

3. The storage tank set forth in claim 1, wherein said heating coils and said manifolds are mounted on the outer surface of said wall structure.

4. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, a plurality of primary heating coils carried by the bottom of said wall structure and disposed on a substantial part of the bottommost portion thereof in surrounding relationship with said output means and each having an inlet and an outlet, a plurality of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils and each having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils. input manifolds interconnecting the outlets of said primary heating coils and the inlets of said secondary heating coils, an output manifold interconnecting the outlets of said secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.

5. The storage tank set forth in claim 4, wherein said output means is disposed centrally of the bottom of said wall structure, the inputs of said primary heating coils being disposed relatively close to said output means and the inputs of said secondary heating coils being disposed relatively distant from said output means.

6. The storage tank set forth in claim 4, and further comprising ajacket surrounding said output means and connected between the inlets of said primary heating coils and said means for introducing heating fluid, whereby the most intense heat is applied directly to said output means.

7. The storage tank set forth in claim 4, wherein said secondary heating coils are divided into two identical groups respectively disposed on opposite sides ofsaid output means.

8. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said wall structure adjacent to said output means and each having an inlet and an outlet, a pair of connecting coils carried by the bottom of said wall structure adjacent to said output means and interconnecting the inlets of said first and second primary heating coils, a plurality of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils and each having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, first and second input manifolds respectively connecting the outlets of said first and second primary heating coils with the inlets of said secondary heating coils, an output manifold interconnecting the outlets of said secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said con necting coils and said primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.

9. The storage tank set forth in claim 8, wherein each of said primary heating coils is arranged in a sinuous form along the bottom of said wall structure.

10. The storage tank set forth in claim 8, wherein said connecting coils are disposed parallel to each other and on opposite sides of said output means.

11. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said wall structure and disposed on opposite sides of said output means and each having an inlet and a pair of outlets, a pair of connecting coils carried by the bottom of said wall structure adjacent to said output means and interconnecting the inlets of said first and second primary heating coils, said pair of connecting coils cooperating with said first and second primary heating coils to circumscribe said output means, four groups of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of secondary coils and each of said secondary coils having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said wall structure and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inputs ofa different one of said four groups of secon- 'dary heating coils, an output manifold interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said connecting coils and primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means andon said bottommost portion of said wall structure.

12. The storage tank set forth in claim 11, and further including auxiliary means disposed adjacent to the inlet of one of said primary heating coils for introducing heating fluid into the inlets of said primary heating coils.

13. The storage tank set forth in claim 11, wherein the cross-sectional areas of said primary heating coils and said connecting coils and said input manifolds are substantially equal to one another and greater than the cross-sectional areas of said secondary heating coils.

14. A heated storage tank comprising an encompassing cylindrical sidewall disposed substantially horizontally, two end walls respectively closing the opposite ends of said sidewall, said cylindrical sidewall and said end walls cooperating to define a closed lading compartment, input means for introducing lading into said lading compartment, output means disposed in the bottom of said cylindrical sidewall substantially midway between the ends thereof for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said cylindrical sidewall and arranged symmetrically with respect to a vertical plane normal to the longitudinal axis thereof midway between the ends thereof and disposed adjacent to said output means and each having an inlet and a pair of outlets, each of said primary heating coils including a plurality of interconnected straight sections extending longitudinally of said cylindrical sidewall, a pair of connecting coils carried by the bottom of said cylindrical sidewall and disposed longitudinally thereof on opposite sides of said output means and interconnecting the inlets of said first and second primary heating coils, four groups of secondary heating coils carried by said cylindrical sidewall and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of coils and each of said coils being disposed substantially longitudinally of said cylindrical sidewall and having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said cylindrical sidewall and extending longitudinally thereof and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inputs of a different one of said four groups of secondary heating coils, an output manifold carried by said cylindrical sidewall and extending circumferentially thereof midway between the ends thereof and interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said primary heating coils and connecting coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.

15. The storage tank set forth in claim 14, wherein each of said primary heating coils includes three parallel longitudinal sections interconnected at the outer ends thereof, the inner ends of the central ones of said sections respectively forming the inlets of said primary heating coils, the inner ends of the side ones of said sections respectively forming the outlets of said primary heating coils.

16. The storage tank set forth in claim 14, wherein each of said input manifolds extends longitudinally of said cylindrical sidewall and substantially to the adjacent end thereof,

17. The storage tank set forth in claim 14, and further including a'pair of short arcuate input coil sections respectively disposed adjacent to the inlets of said first and second primary heating coils and extending circumferentially of said cylindrical sidewall, each of said input coil sections communicating with the inlet of the adjacent primary heating coils and with the adjacent ends of said pair of connecting coils, and at least one ofsaid input coil sections communicating directly with said means for introducing heating fluid to said primary coils.

18. The storage tank set forth in claim 14, wherein each of said secondary heating coils includes a relatively long straight section extending longitudinally of said cylindrical sidewall and a relatively short arcuate section integral with said long straight section at the outer end thereof and extending circumferentially downwardly along said cylindrical sidewall, the inner ends of said long straight sections communicating with said output manifold and the lower ends of said short arcuate sections communicating with the corresponding one of said input manifolds.

[9. A vehicle comprising a wheeled chassis, an encompassing cylindrical sidewall carried by said chassis and disposed substantially horizontally, two end walls respectively closing the opposite ends of said sidewall, said cylindrical sidewall and said end walls cooperating to define a closed lading compartment, input means for introducing lading into said lading compartment, output means disposed in the bottom of said cylindrical sidewall substantially midway between the ends thereof for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said cylindrical sidewall and arranged symmetrically with respect to a vertical midplane normal to the longitudinal axis thereof midway between the ends thereof and disposed adjacent to said output means and each having an inlet and a pair of outlets, each of said primary heating coils including a plurality of interconnected straight sections extending longitudinally of said cylindrical sidewall, a pair of connecting coils carried by the bottom of said cylindrical sidewall and disposed longitudinally thereof on opposite sides of said output means and interconnecting the inlets of said first and second primary heating coils, four groups of secondary heating coils carried by said cylindrical sidewall and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of coils and each of said secondary coils being disposed substantially longitudinally of said cylindrical sidewall and having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said cylindrical sidewall and extending longitudinally thereof and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inlets of a different one of said four groups of secondary heating coils, an output manifold carried by said cylindrical sidewall and extending circumferentially thereof midway between the ends thereof and interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said connecting coils and primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.

20. The vehicle set forth in claim 19, wherein said vehicle comprises a railway tank car. 

1. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, an input manifold carried by the bottom of said wall structure, in close proximity to said output means, an output manifold carried by the bottom of said wall structure and crossing over said input manifold intermediate the ends thereof, said input manifold and said output manifold cooperating to define four sectors on the bottom of said wall structure, four groups of heating coils carried by said wall structure adjacent to the bottom thereof and being arranged on a substantial part of the bottommost portion of said wall structure, each of said groups of coils being limited to a different one of said sectors and communicating with said input manifold and said output manifold, means for introducing heating fluid into said input manifold, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried from said input manifold through said heating coils to said output manifold for heating the bottom of said storage tank and the lading contained therein.
 2. The storage tank set forth in claim 1, wherein said input manifold and said output manifold are disposed substantially perpendicular to each other, said manifolds crossing each other midway between the ends thereof.
 3. The storage tank set forth in claim 1, wherein said heating coils and said manifolds are mounted on the outer surface of said wall structure.
 4. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, a plurality of primary heating coils carried by the bottom of said wall structure and disposed on a substantial part of the bottommost portion thereof in surrounding relationship with said output means and each having an inlet and an outlet, a plurality of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils and each having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, input manifolds interconnecting the outlets of said primary heating coils and the inlets of said secondary heating coils, an output manifold interconnecting the outlets of said secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.
 5. The storage tank set forth in claim 4, wherein said output means is disposed centrally of the bottom of said wall structure, the inputs of said primary heating coils being disposed relatively close to said output means and the inputs of said secondary heating coils being disposed relatively distant from said output means.
 6. The storage tank set forth in claim 4, and further comprising a jacket surrounding said output means and connected between the inlets of said primary heating coils and said means for introducing heating fluid, whereby the most intense heat is applied directly to said output means.
 7. The storage tank set forth in claim 4, wherein said secondary heating coils are divided into two identical groups respectively disposed on opposite sides of said output means.
 8. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said wall structure adjacent to said output means and each having an inlet and an outlet, a pair of connecting coils carried by the bottom of said wall structure adjacent to said output means and interconnecting the inlets of said first and second primary heating coils, a plurality of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils and each having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, first and second input manifolds respectively connecting the outlets of said first and second primary heating coils with the inlets of said secondary heating coils, an output manifold interconnecting the outlets of said secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said connecting coils and said primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.
 9. The storage tank set forth in claim 8, wherein each of said primary heating coils is arranged in a sinuous form along the bottom of said wall structure.
 10. The storage tank set forth in claim 8, wherein said connecting coils are disposed parallel to each other and on opposite sides of said output means.
 11. A heated storage tank comprising an encompassing wall structure defining therein a lading compartment, input means for introducing lading into said lading compartment, output means in the bottom of said wall structure for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said wall structure and disposed on opposite sides of said output means and each having an inlet and a pair of outlets, a pair of connecting coils carried by the bottom of said wall structure adjacent to said output means and interconnecting the inlets of said first and second primary heating coils, said pair of connecting coils cooperating with said first and second primary heating coils to circumscribe said output means, four groups of secondary heating coils carried by said wall structure and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of secondary coils and each of said secondary coils having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said wall structure and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inputs of a different one of said four groups of secondary heating coils, an output manifold interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said connecting coils and primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.
 12. The storage tank set forth in claim 11, and further including auxiliary means disposed adjacent to the inlet of one of said primary heatIng coils for introducing heating fluid into the inlets of said primary heating coils.
 13. The storage tank set forth in claim 11, wherein the cross-sectional areas of said primary heating coils and said connecting coils and said input manifolds are substantially equal to one another and greater than the cross-sectional areas of said secondary heating coils.
 14. A heated storage tank comprising an encompassing cylindrical sidewall disposed substantially horizontally, two end walls respectively closing the opposite ends of said sidewall, said cylindrical sidewall and said end walls cooperating to define a closed lading compartment, input means for introducing lading into said lading compartment, output means disposed in the bottom of said cylindrical sidewall substantially midway between the ends thereof for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said cylindrical sidewall and arranged symmetrically with respect to a vertical plane normal to the longitudinal axis thereof midway between the ends thereof and disposed adjacent to said output means and each having an inlet and a pair of outlets, each of said primary heating coils including a plurality of interconnected straight sections extending longitudinally of said cylindrical sidewall, a pair of connecting coils carried by the bottom of said cylindrical sidewall and disposed longitudinally thereof on opposite sides of said output means and interconnecting the inlets of said first and second primary heating coils, four groups of secondary heating coils carried by said cylindrical sidewall and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of coils and each of said coils being disposed substantially longitudinally of said cylindrical sidewall and having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said cylindrical sidewall and extending longitudinally thereof and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inputs of a different one of said four groups of secondary heating coils, an output manifold carried by said cylindrical sidewall and extending circumferentially thereof midway between the ends thereof and interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said primary heating coils and connecting coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.
 15. The storage tank set forth in claim 14, wherein each of said primary heating coils includes three parallel longitudinal sections interconnected at the outer ends thereof, the inner ends of the central ones of said sections respectively forming the inlets of said primary heating coils, the inner ends of the side ones of said sections respectively forming the outlets of said primary heating coils.
 16. The storage tank set forth in claim 14, wherein each of said input manifolds extends longitudinally of said cylindrical sidewall and substantially to the adjacent end thereof.
 17. The storage tank set forth in claim 14, and further including a pair of short arcuate input coil sections respectively disposed adjacent to the inlets of said first and second primary heating coils and extending circumferentially of said cylindrical sidewall, each of said input coil sections communicating with the inlet of the adjacent primary heating coils and with the adjacent ends of said pair of connecting coils, and at least one of said input coil sections communicating directly with said means for introducing heating fluid to said primary coils.
 18. The storage tank set forth in claim 14, wherein each of said secondary heating coils includes a relatively long straight section extending longitudinally of said cylindrical sidewall and a relatively short arcuate section integral with said long straight section at the outer end thereof and extending circumferentially downwardly along said cylindrical sidewall, the inner ends of said long straight sections communicating with said output manifold and the lower ends of said short arcuate sections communicating with the corresponding one of said input manifolds.
 19. A vehicle comprising a wheeled chassis, an encompassing cylindrical sidewall carried by said chassis and disposed substantially horizontally, two end walls respectively closing the opposite ends of said sidewall, said cylindrical sidewall and said end walls cooperating to define a closed lading compartment, input means for introducing lading into said lading compartment, output means disposed in the bottom of said cylindrical sidewall substantially midway between the ends thereof for emptying lading from said lading compartment, first and second primary heating coils carried by the bottommost portion of said cylindrical sidewall and arranged symmetrically with respect to a vertical midplane normal to the longitudinal axis thereof midway between the ends thereof and disposed adjacent to said output means and each having an inlet and a pair of outlets, each of said primary heating coils including a plurality of interconnected straight sections extending longitudinally of said cylindrical sidewall, a pair of connecting coils carried by the bottom of said cylindrical sidewall and disposed longitudinally thereof on opposite sides of said output means and interconnecting the inlets of said first and second primary heating coils, four groups of secondary heating coils carried by said cylindrical sidewall and disposed adjacent to said primary heating coils, each of said groups including the same predetermined number of coils and each of said secondary coils being disposed substantially longitudinally of said cylindrical sidewall and having an inlet and an outlet, means for introducing heating fluid into the inlets of said primary heating coils, four input manifolds carried by said cylindrical sidewall and extending longitudinally thereof and each having an inlet and a plurality of outlets equal in number to said predetermined number, the inlets of said input manifolds respectively communicating with the outlets of said first and second primary heating coils, the outlets of each of said input manifolds respectively communicating with the inlets of a different one of said four groups of secondary heating coils, an output manifold carried by said cylindrical sidewall and extending circumferentially thereof midway between the ends thereof and interconnecting the outlets of said four groups of secondary heating coils, and means for withdrawing spent heating fluid from said output manifold, whereby heating fluid is carried first to said connecting coils and primary heating coils and thence through said input manifolds to said secondary heating coils and thence to said output manifold for heating the bottom of said storage tank and the lading contained therein with the most intense heating being adjacent to said output means and on said bottommost portion of said wall structure.
 20. The vehicle set forth in claim 19, wherein said vehicle comprises a railway tank car. 